TY - JOUR A1 - Tabin, J. A1 - Kawałko, J. A1 - Schob, Daniela A1 - Roszak, R. A1 - Brodecki, A. A1 - Bała, P. A1 - Maasch, philipp A1 - Kowalewski, Z. A1 - Ziegenhorn, M. T1 - Deformation-induced martensitic transformation in fused filament fabrication austenitic stainless steels during tension at wide range of temperatures (77 K, RT) N2 - This study investigates the mechanical behaviour of fused filament fabrication (FFF) of 316L austenitic stainless steel compared to conventional 316L at room temperature and 77 K, focusing on deformation-induced martensitic transformation (DIMT). Results reveal that the Lüders-like effect, present in conventional 316L at 77 K, is absent in FFF 316L due to porosities that hinder martensitic front propagation. At room temperature, uniform strain distribution and DIMT were observed in conventional 316L, whereas in FFF 316L, martensitic nucleation occurred around pores, serving as a localized strengthening mechanism. Microstructural analysis identified Fe-δ islands along grain boundaries in FFF 316L, which contribute to its multiphase nature. Although FFF 316L demonstrates lower yield stress and elongation compared to conventional 316L, this study does not establish design allowables. The present findings are limited to monotonic tensile behaviour, fatigue performance and corrosion resistance under cryogenic conditions were not assessed. Further optimization of fabrication parameters to minimize ferrite content and porosities is suggested to enhance mechanical performance. KW - TRIP effect KW - Fused filament fabrication KW - 316L KW - Cryogenic KW - Cryogenic temperatures KW - Microstructure PY - 2026 DO - https://doi.org/10.1016/j.msea.2025.149552 SN - 0921-5093 VL - 950 SP - 1 EP - 13 PB - Elsevier B.V. AN - OPUS4-65141 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Huber, Norbert T1 - Machine Learning Approaches for Intentional Materials Engineering N2 - The development of nanoporous metals and metallic composites through dealloying processes presents significant opportunities in materials engineering. However, designing multicomponent precursor alloys and establishing corresponding processing methods that yield predictable compositions and nanostructures remain a complex challenge. The talk explores how machine learning (ML)-augmented computational and experimental methodologies can tackle these challenges by predicting precursor alloy compositions, final nanoporous structures, and mechanical properties, while integrating ML-enabled autonomous experimentation for material design and quantification. Recent advancements in applying ML to nanostructured materials design will be touched along with techniques from other nanomaterial designs that can be adapted for improved control over morphological and compositional outcomes in nanoporous and nanocomposite materials. The focus of the talk will be set on ML-driven approaches to microstructure characterization and mechanical property prediction, modeling, and advanced imaging techniques such as three-dimensional nanotomography. Finally, the talk outlines future directions for ML-enhanced materials science, emphasizing the exploration of high-dimensional parameter spaces and the incorporation of materials kinetics into processing and property evaluation, ultimately advancing the design of nanoporous structures and materials science. T2 - MSE Research Data Forum 2025 CY - Siegburg, Germany DA - 08.07.2025 KW - Nanoporous Metals KW - Machine Learning KW - Microstructure KW - Mechanical Properties KW - Structure-Properties-Relationship PY - 2025 AN - OPUS4-63919 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael T1 - Weld heat input effect on microstructure and hydrogen diffusion in thick-walled S690 submerged arc welded joints N2 - High-strength, low-alloy (HLSA) steels such as S690 are an attractive option for heavy industries such as offshore wind turbines and peripheral equipment due to their combination of excellent mechanical properties and weldability. The construction of these thick-walled structures requires highly efficient welding processes such as submerged arc welding (SAW). However, SAW faces challenges related to delayed hydrogen assisted cold cracking (HACC). Despite its importance, the effect of different diffusion coefficients on the cold cracking susceptibility of different microstructures within SAW-welded S690 steels is not fully understood. For this reason, the present study focuses on comparing the cold cracking susceptibility of thermomechanically rolled (TM) or quenched and tempered (QL) variants of S690 steel. Submerged arc welding was performed on both steel grades at different welding heat inputs. From these thick-walled welds, metallic membranes were extracted from the weld metal, the heat-affected zone (HAZ), and the two base metals. The specimens were subjected to electrochemical hydrogen permeation tests (according to ISO 17081) to determine the microstructure-specific hydrogen diffusion coefficients. In general, increased welding heat input and thickness decreased the hydrogen diffusion coefficients, i.e., the time required for hydrogen diffusion increased. In addition, the results showed that the TM grade exhibited slightly accelerated hydrogen diffusion coefficients compared to the QL grade, which is beneficial for hydrogen reduction and increases the HACC resistance. As a result, the microstructure-specific assessment of hydrogen diffusion in the BM, HAZ or WM of the SAW joint was less important for a given set of welding parameters compared to other welding processes such as gas metal arc welding (GMAW). The reason is that in multilayer SAW, the relatively large welding heat input and multiple annealing resulted in similar microstructures, resulting in very close hydrogen diffusion coefficients. From this point of view, it is sufficient to characterize the hydrogen diffusion coefficients of both the weld metal and the base material. T2 - 78th IIW Annual Assembly and International Conference CY - Genoa, Italy DA - 26.06.2025 KW - Hydrogen assisted cracking KW - Submerged arc welding KW - Diffusion KW - Electrochemical permeation KW - Microstructure PY - 2025 AN - OPUS4-63543 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rhode, Michael T1 - Ti and Nb influence on the HAZ microstructures of weld-simulated high-strength structural steel S690QL N2 - High-strength low-alloyed (HSLA) steels with yield strength / proof stress ≥ 600 MPa are the basis of modern light-weight steel constructions. Indeed, the economic and ecological benefits strongly depend on their processability in terms of welding. In this context, the use of highly productive welding processes, suitable welding consumables is of vital interest and requires a fundamental understanding of the microstructural changes in the HSLA steel and especially the heat-affected zone (HAZ) of the welded joint. Microalloying elements, such as Ti or Nb, are essential to achieve the desired mechanical properties. In this context, the underlying standards (such as EN 10025-6) only specify maximum values, resulting in different manufacturer customized microalloy concepts. Furthermore, even small deviations can have a drastic effect expressed by an excessive hardening or softening despite identical welding conditions and filler metal. The reason is the different thermal stability of the Ti and Nb-related precipitates (typically carbides or carbon nitrides). As a result, it is difficult (or even impossible) to adequately predict the weldability. Against this background, different microalloying routes with varying Ti and Nb contents for a S690QL reference grade were systematically investigated in terms of lab-cast alloys close to realistic chemical compositions. To investigate the influence of the welding heat input on the HAZ microstructure formation, physical simulations were carried with specified peak temperatures and cooling times (by a dilatometry). The focus was the identification of the occurring phase transformations during cooling and the final HAZ microstructure. In this context, a double welding cycle was simulated to further identify the behavior of the so-called intercritical HAZ (where softening is likely to occur) in case of the common multi-layer welding for thick plates. The results showed: (1) microalloying has significant influence on the formation of the individual HAZ dependent on (2) the thermal stability of the Ti or Nb-precipitates and (3) synergistic effects of further elements such as Mo and their effect on phase transformations in the HAZ. The results represent a microstructure-based validation of welding processing of such HSLA-steels e.g. in terms of preferred microalloy and weld heat input combinations. T2 - 49th MPA Conference CY - Stuttgart, Germany DA - 06.10.2025 KW - High-strength steel KW - Microalloy elements KW - Welding KW - Weld simulation KW - Microstructure PY - 2025 AN - OPUS4-64319 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Suarez Ocano, Patricia T1 - Influence of heat-treatment-induced microstructural evolution on the Low Cycle Fatigue behavior of 316L stainless steel fabricated by Laser Powder Bed Fusion N2 - Additive manufacturing, particularly the laser powder bed fusion (PBF-LB/M) process, has gained significant attention in recent years due to its ability to produce complex geometries with enhanced mechanical properties. Among the various materials used, 316L stainless steel is highly favored for cyclically loaded components due to its exceptional mechanical strength, high-temperature performance, and corrosion resistance, making it widely applicable across various industries. 316L SS fabricated by PBF-LB/M (PBF-LB/M/316L) exhibits a unique hierarchical microstructure, with high density of low-angle grain boundaries (LAGBs), nano-dispersed silicates, chemical micro-segregations, and solidification-induced cellular structures. Particularly, the submicron-sized cellular features enriched with chromium (Cr) and molybdenum (Mo), along with high dislocation densities, contribute to a superior strength-ductility balance compared to conventionally manufactured 316L SS. The dispersed silicate particles act also as a strengthening phase, impeding dislocation movement and enhancing plastic deformation resistance. This study explores the effect of heat treatments on the low-cycle fatigue (LCF) behavior of PBF-LB/M/316L at room temperature (RT) and 600 °C. First, three heat treatment conditions were applied to the as-built material: 450 °C for 4 hours (HT450/4), 800 °C for 3 hours (HT800/3), and 900 °C for 1 hour (HT900/1) to investigate their influence on microstructural evolution. Microstructural analysis revealed that the HT450/4 condition preserved the cellular structure with high dislocation density, while the HT800/3 condition showed partial dissolution of cells together with reduction in segregated elements along the cell walls and a reduced dislocation density. The HT900/1 condition resulted in complete segregation and cellular structure dissolution with comparable dislocation density to HT800/3 while maintaining the crystallographic texture and grain morphology. Intermetallic χ phase was mostly observed at the grain boundaries in HT800/3, but not in HT900/1. Fully reversed LCF tests were conducted under strain-controlled conditions with a strain amplitude of 0.8 %. Tests were interrupted at specific intervals to analyze the interaction between hierarchical microstructural features and deformation mechanisms in the three heat-treated conditions. Due to the pronounced dislocation cell structures and elemental segregation, the microstructure of the HT450/4 condition significantly impact deformation and damage mechanisms during cyclic loading, which in turn, differ from the conventional produced counterparts. The results provide insights into the relationship between microstructural features and fatigue performance, highlighting key deformation and failure mechanisms under cyclic loading. T2 - FEMS 2025 EUROMAT 18th European Congress and Exhibition on Advanced Materials and Processes CY - Granada, Spain DA - 14.09.2025 KW - Additive manufacturing KW - 316L stainless steel KW - Heat treatments KW - Low Cycle Fatigue KW - Microstructure PY - 2025 AN - OPUS4-64238 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Evans, Alexander A1 - Schröder, Jakob A1 - Pirling, T. A1 - Ulbricht, Alexander A1 - Suárez Ocaño, Patricia A1 - Bruno, Giovanni T1 - Resolving the Subsurface Residual Stress Maximum in Laser Powder Bed-Fused 316L Stainless Steel by Diffraction-Based Analysis N2 - Laser powder bed fusion (PBF-LB/M) is a metal additive manufacturing process. Due to the complex nature of the layer-wise, repeated heating and cooling cycles, it tends to generate high-magnitude residual stresses. If not correctly understood and mitigated through in- or post-process approaches, these residual stresses can be detrimental as they are often tensile at the surface. However, determining the magnitude and location of peak tensile residual stresses is not trivial as they are often located subsurface. This work focuses on determining the magnitude and location of these deleterious tensile residual stresses in a PBF-LB/316L specimen. Two diffraction-based Methods are used to reveal the relationship between the residual stresses and the underlying microstructure. On the one hand, high spatial resolution Neutron diffraction is used to determine triaxial stresses from the bulk to a depth of 0.15 mm. On the other hand, laboratory X-ray diffraction coupled with electrolytical layer removal allows the biaxial residual stress depth profile to be probed from the surface to a depth of about 0.6 mm. The results show a good agreement between the two methods. The peak residual stress is shown to be 500 MPa, which appears as a plateau between 0.08 and 0.35 mm in depth. KW - Residual stress KW - Diffraction KW - Laser Powder Bed Fusion KW - 316L KW - Additive manufacturing KW - Microstructure KW - AGIL PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-652138 DO - https://doi.org/10.1007/s11837-025-07719-y SN - 1543-1851 VL - 77 IS - 12 SP - 9726 EP - 9737 PB - Springer Nature AN - OPUS4-65213 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ávila Calderón, Luis T1 - Creep Behavior of Stainless Steel 316L Manufactured by Laser Powder Bed Fusion N2 - The broader industrial adoption of metal AM in safety-critical applications is limited, among others, by the still in-sufficient understanding of process–structure–property relationships and a lack of reliable mate-rial data. The content presented here approaches this limitation regarding the creep behavior of one of the most studied AM alloys: PBF-LB/M/316L stainless steel. A nearly as-built and a condition heat treated at 900 °C for 1 h, along with a conventionally manufactured variant are investigated. The creep behavior until reaching the minimum creep rate is mainly determined by the solidification cell structure. The damage is overall mainly intergranular, independent of the heat treated condition. The heat treatment at 900 °C for 1 h partially influenced the microstructure (mainly in terms of cell structure). The creep behavior until reaching the minimum creep rate remained nearly unchanged. The creep lifetime and ductility were enhanced. The crystallographic texture evolved after creep deformation. T2 - TMS 2025 Annual Meeting & Exhibition CY - Las Vegas, NV, USA DA - 23.03.2025 KW - AGIL KW - Creep KW - 316L KW - Microstructure PY - 2025 AN - OPUS4-63456 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Beygi Nasrabadi, Hossein A1 - Klotz, Ulrich E. A1 - Tiberto, Dario A1 - Vafaeenezhad, Hossein A1 - Mishurova, Tatiana A1 - Skrotzki, Birgit T1 - Effect of keyhole and lack-of-fusion pores on the anisotropic microstructure and mechanical properties of PBF-LB/M-produced CuCrZr alloy N2 - Due to the high reflectance and heat conductivity of copper and its alloys, the processing window for laser-based powder bed fusion (PBF-LB/M) processing of high-density copper components fundamentally overlaps with conduction and keyhole melting zones, resulting in the emergence of certain pores in the structure of printed parts. The present research aims to study how the development of process-induced lack-of-fusion or keyhole porosities during the PBF-LB/M process can affect the anisotropic microstructure and mechanical properties of the produced copper alloys. For this purpose, several samples were produced utilizing a similar CuCrZr-feedstock composition but varied process parameters from different areas of the PBF-LB/M processing window, specifically at laser powers of 300 W and 380 W which define the boarders of the conduction and keyhole regimes. X-ray computed tomography (XCT) revealed that the 300-W and 380-W samples achieved relative densities of 98.88% and 99.99%, respectively, with elongated lack-of-fusion pores forming at 300 W and semi-spherical keyhole pores at 380 W. Microstructural analyses employing scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) demonstrated strong anisotropy in different build directions of the samples, owing to the growth of long columnar grains with intense < 101  orientation along the build directions. Here, the emergence of different types of pores can cause competition between the epitaxial growth of columnar grains and the heterogeneous nucleation of new grains on the layers’ interfaces, thereby significantly varying the grain size, preferred orientation, crystallographic texture, and microstructural anisotropy of the samples. Furthermore, compression tests and nanoindentation measurements of the printed alloys in the longitudinal and transverse directions revealed that the 300 W and 380 W samples exhibited compressive strength anisotropies of 0.061 and 0.072, and average nanoindentation hardness values of 1.3 GPa and 1.5 GPa, respectively. The orientation of elongated lack-of-fusion porosities perpendicular to the loading axis was identified as the most damaging factor, significantly reducing mechanical performance compared to the uniformly distributed keyhole pores. KW - Copper Alloy KW - Laser-based powder bed fusion KW - Microstructure KW - Mechanical properties KW - X-ray computed tomography (XCT) KW - Porosity KW - Anisotropy PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-625655 DO - https://doi.org/10.1007/s40964-025-00972-2 SN - 2363-9520 SP - 1 EP - 15 PB - Springer Science and Business Media LLC AN - OPUS4-62565 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Suárez Ocaño, Patricia A1 - Ávila Calderón, Luis A1 - Agudo Jácome, Leonardo A1 - Rehmer, Birgit A1 - Mohr, Gunther A1 - Evans, Alexander A1 - Skrotzki, Birgit T1 - Effect of 700–900 °C heat treatments and room and high temperature tensile deformation on the microstructure of laser powder bed fused 316L stainless steel N2 - The effect of post-processing heat treatments on the hierarchical microstructure evolution and mechanical strength of the austenitic stainless steel 316L produced by laser powder bed fusion has been investigated. Heat treatments between 700 and 900 ◦C and 0.5 to 3 h, were applied to samples treated at 450 ◦C for 4 h. The results showed a stable microstructure at all studied temperatures and times in terms of grain size, morphology, aspect ratio, density of low-angle grain boundaries, and texture. However, temperature and time promoted the diffusion of segregated elements together with a reduction in dislocation density and disappearance of the cellular structure. This was associated with a reduction in hardness and tensile proof strength at both room and high temperature. In addition, microstructural characterization coupled with thermodynamic CALPHAD-based equilibrium calculations showed that the formation of carbides and intermetallic phases was already visible after annealing at 800 ◦C for 3 hours, although these intermetallics did not affect the tensile properties at this level. Analysis of the microstructure evolution after tensile deformation showed differences in the deformation mechanisms at room and high temperature, with twinning and martensitic transformation occurring at room temperature, the latter not widely reported for additively manufactured 316L. Finally, comparisons with similar materials produced under comparable conditions showed differences in the tensile properties, attributed to differences in chemical composition and the associated presence of stacking faults in the undeformed state. KW - Additive manufacturing KW - 316L stainless steel KW - Heat treatments KW - Tensile properties KW - Microstructure PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-632471 DO - https://doi.org/10.1016/j.msea.2025.148469 SN - 0921-5093 VL - 939 SP - 1 EP - 24 PB - Elsevier CY - Amsterdam AN - OPUS4-63247 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Campos de Oliveira, Paula T1 - Advancing microstructural characterisation of ceramic cores for aerospace: from state-of-the-art to in-situ synchrotron X-ray computed tomography N2 - Ceramic cores are crucial for manufacturing turbine blades in aircraft engines, creating intricate cooling channels that improve engine efficiency and reduce emissions. During high-temperature casting, the cores undergo significant microstructural changes, including phase transitions, particle rearrangements, and porosity transformations, which can affect their properties and must be carefully controlled. State-of-the-art characterisation techniques for ceramic cores mostly rely on 2D methods, such as scanning and transmission electron microscopy. While valuable, these methods are limited in capturing the 3D complexity of the material. Advances in X-ray computed tomography (XCT) offer a more comprehensive perspective on 3D microstructures, but conventional XCT often lacks the resolution and in-situ capabilities to study microstructural evolution under casting conditions. Synchrotron XCT (SXCT) addresses these limitations, offering high spatial and temporal resolution with features down to 1 µm, enabling in-situ investigations. This study highlights the potential of SXCT, revealing previously unseen 3D microstructural features in ceramic cores, such as agglomeration, porosity evolution, surface reactions, microcracking, and particle orientation. These findings provide a more realistic view of dynamic changes during casting, advancing the understanding of core behaviour. Despite its advantages, SXCT is still rarely used in the field due to challenges such as limited access to synchrotron facilities and sample movement artifacts. Future developments, including high-temperature and vacuum compatible CT setups, could enhance this technique, leading to a better optimisation of ceramics performance. T2 - XIXth Conference of the European Ceramic Society (ECERS 2025) CY - Dresden, Germany DA - 31.08.2025 KW - Synchrotron KW - X-ray Computed Tomography KW - Ceramic core KW - Aerospace KW - Microstructure PY - 2025 AN - OPUS4-64050 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -